The device can comprise sensors, making it possible to determine the movement of the mobile elements. These sensors, such as, for example, position, speed or acceleration sensors, are secured to the mobile elements and have to transmit the measured information to the fixed element. Other types of sensors, allowing a particular physical quantity to be measured, can also equip the mobile elements. As an example, an articulated arm can bear an environment sensor (temperature, pressure, etc.). The movement of the arm allows particular zones of space to be reached.
All these sensors generally return the measured information to the fixed element of the device to be processed therein.
The solution most commonly employed for the transmission of information between a mobile sensor and a fixed element consists in connecting the sensor by means of electric cables. The electrical cables run along link elements linking the fixed element to the mobile element bearing the sensor. The cables have to pass through the articulations linking the different elements to one another.
These cables risk being damaged when using the device, for example by catching on an external object. Furthermore, the cables often convey electrical signals of low intensity, likely to be disturbed by the electromagnetic environment. For example, the sensors of piezoelectric type deliver particularly low signals. The cables associated with these sensors cannot be of great length without degrading the information from the sensor.
In the particular case of a cylinder in which a stem is moved in translation in relation to a body of the cylinder, it is common practice to arrange, on the stem, a sensor allowing the position of the stem to be determined in relation to the body. The sensor is connected by a cable to the body of the cylinder. The conventional cylinders have symmetry of revolution and the stem remains free in rotation about the axis of translation of the cylinder. This freedom in rotation can be detrimental to the cable which risks being wound around the stem. There is then a need to provide a stem rotation prevention device, which pointlessly complicates the cylinder.
It has also been considered to provide a wireless link, for example by radio, between the sensor and the fixed element. This type of link is suitable for the data from the sensor, but remains subject to electromagnetic interference. Furthermore, the supply of energy to the sensor is not assured. It is then necessary to provide a battery secured to the sensor to power it. This battery needs to have a sufficient life to ensure the operation of the sensor and the transmission of information to the fixed element. It is also necessary to periodically provide for the recharging of the battery or the replacement thereof, which results in an increase in the cost of operation of the device.